Reverse Polarity Cleaning and Electronic Flow Control Systems for Low Intervention Electrolytic Chemical Generators

ABSTRACT

Method and apparatus for a low maintenance, high reliability on-site electrolytic generator incorporating automatic cell monitoring for contaminant film buildup, as well as automatically removing or cleaning the contaminant film. This method and apparatus preferably does not require human intervention to clean. For high current density cells, cleaning is preferably performed by reversing the polarity of the electrodes and applying a lower current density to the electrodes. A second lower current density power supply may be used for reverse polarity cleaning. Electrolyte flow is preferably monitored and automatically adjusted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of filing of U.S.Provisional Patent Application Ser. No. 61/056,718, entitled “ReversePolarity Cleaning for High Current Density Electrolytic Cells,” filed onMay 28, 2008. This application is also a continuation-in-partapplication of U.S. patent application Ser. No. 11/946,772, entitled“Low Maintenance On-Site Generator”, filed on Nov. 28, 2007, whichapplication claims priority to and the benefit of filing of U.S.Provisional Patent Application Ser. No. 60/867,557, entitled “LowMaintenance On-Site Generator”, filed on Nov. 28, 2006. Thespecification and claims of all of these applications are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to an electrolytic on-site generator whichis nearly free of maintenance.

2. Background Art

Note that the following discussion refers to a number of publicationsand references. Discussion of such publications herein is given for morecomplete background of the scientific principles and is not to beconstrued as an admission that such publications are prior art forpatentability determination purposes.

Electrolytic technologies utilizing dimensionally stable anodes havebeen developed to produce mixed-oxidants and sodium hypochloritesolutions from a sodium chloride brine solution. Dimensionally stableanodes are described in U.S. Pat. No. 3,234,110 to Beer, entitled“Electrode and Method of Making Same,” wherein a noble metal coating isapplied over a titanium substrate. Electrolytic cells have had wide usefor the production of chlorine and mixed oxidants for the disinfectionof water. Some of the simplest electrolytic cells are described in U.S.Pat. No. 4,761,208, entitled “Electrolytic Method and Cell forSterilizing Water”, and U.S. Pat. No. 5,316,740, entitled “ElectrolyticCell for Generating Sterilizing Solutions Having Increased OzoneContent.”

Electrolytic cells come in two varieties. The first category comprisesdivided cells that utilize membranes to maintain complete separation ofthe anode and cathode products in the cells. The second categorycomprises undivided cells that do not utilize membranes, but that alsodo not suffer nearly as much from issues associated with membranefouling. However, it is well accepted that one of the major failuremechanisms of undivided electrolytic cells is the buildup of unwantedfilms on the surfaces of the electrodes. The source of thesecontaminants is typically either from the feed water to the on-sitegeneration process or contaminants in the salt that is used to producethe brine solution feeding the system. Typically these unwanted filmsconsist of manganese, calcium carbonate, or other unwanted substances.If buildup of these films is not controlled or they are not removed on afairly regular basis, the electrolytic cells will lose operatingefficiency and will eventually catastrophically fail (due to localizedhigh current density, electrical arcing or some other event). Typically,manufacturers protect against this type of buildup by incorporating awater softener on the feed water to the system to prevent thesecontaminants from ever entering the electrolytic cell. However, thesecontaminants will enter the process over time from contaminants in thesalt used to make the brine. High quality salt is typically specified tominimize the incidence of cell cleaning operations. Processes are wellknown in the art for purifying salt to specification levels that willavoid contaminants from entering the cell. However, these salt cleaningprocesses, although mandatory for effective operation of divided cells,are considered too complicated for smaller on-site generation processesthat utilize undivided cells.

U.S. patent application Ser. No. 11/287,531, which is incorporatedherein by reference, is directed to a carbonate detector and describesone possible means of monitoring an electrolytic cell for internal filmbuildup. Other possible means for monitoring carbonate buildup in cellsthat utilize constant current control schemes is by monitoring the rateof brine flow to the cell. As brine flow increases, it is usually, butnot always, indicative of carbonate formation on the cathode electrodewhich creates electrical resistance in the cell. Other than thesemethods and/or visual inspection of the internal workings of a cell,there currently is not an adequate method of monitoring the internalstatus of the buildup on an electrolytic cell.

The current accepted method of cleaning an electrolytic cell is to flushit with an acid (often muriatic or hydrochloric acid) to remove anydeposits which have formed. Typically, manufacturers recommendperforming this action on a regular basis, at least yearly, butsometimes as often as on a monthly basis. Thus there is a need for amore reliable method for insuring cleanliness of the electrolytic cellis to perform a cleaning process on an automated basis that does notrequire the use of a separate supply of consumables such as muriatic orhydrochloric acid, and that does not require operator intervention.

U.S. Pat. No. 5,853,562 to Eki, et al. entitled “Method and Apparatusfor Electrolyzing Water” describes a process for reversing polarity onthe electrodes in a membraneless electrolytic cell for the purpose ofremoving carbonate scale and extending the life of the electrolyticcell. This method of electrolytic cell cleaning is routinely used inflow through electrolytic chlorinators that convert sodium chloride saltin swimming pool water to chlorine via electrolysis. However, currentlyused flow through electrolytic cells are constructed of electrodes(anode and cathode) that both have common catalytic coatings. Aselectrical polarity is changed, the old cathode becomes the anode, andthe anode becomes the cathode. Special catalytic coatings have beendeveloped for these applications. For instance, Eltech Corporation hasdeveloped the EC-600 coating specifically for the swimming poolchlorination market. Sodium chloride is typically added to the poolwater raising the total dissolved solids (TDS) content to approximately4 to 5 grams per liter. At these TDS values, the current density in theswimming pool electrolytic cells is relatively low. The special anodecoatings for pool applications are designed to tolerate these lowcurrent densities for extended periods with polarity applied in eitherdirection. However, most dimensionally stable anodes for chlorineproduction in membraneless electrolytic cells producing chlorine at 8gram per liter (8,000 mg/L) concentration of free available chlorine(FAC) cannot tolerate high current densities (greater than approximately1 amp per square inch) in reverse polarity mode. Thus, although simplyreversing the polarity works for low current density electrolytic cells,it will not work for electrolytic cells which normally operate at a highcurrent density, since the anode will be damaged if high current densityis applied during the reverse polarity cleaning operation.

One of the other maintenance items for electrolytic generators is therequirement that operators occasionally measure and set water flow intothe system. The flow through the generator can vary greatly withincoming and outgoing water pressure and/or contaminant buildup in thesystem or electrolytic cells. Typically, measurements are made witheither flowmeters or with timed volume measurements, and adjustments tothe flow are performed with manual valves. Keeping the electrolyticgenerator operating within flow specifications is important, as itensures reliable long term operation the generator within its efficiencyspecifications.

SUMMARY OF THE INVENTION Disclosure of the Invention

The present invention is a method for operating an electrolytic cell,the method comprising the steps of supplying brine to an electrolyticcell, producing one or more oxidants in the electrolytic cell, detectinga level of contaminant buildup, automatically stopping the brine supplyafter an upper contaminant threshold is detected, automatically cleaningthe electrolytic cell, thereby reducing contaminants in the electrolyticcell, and automatically continuing to produce the one or more oxidantsafter a lower contaminant threshold is detected. The cleaning steppreferably comprises providing brine to an acid generating electrolyticcell, generating an acid in the acid generating electrolytic cell, andintroducing the acid into the electrolytic cell. The acid preferablycomprises muriatic acid or hydrochloric acid. The method preferablyfurther comprises the step of diluting the brine. The detecting steppreferably comprises utilizing a carbonate detector. The detecting steppreferably comprises measuring the rate of brine consumption in theelectrolytic cell, optionally by measuring a quantity selected from thegroup consisting of flow meter output, temperature of the electrolyticcell, brine pump velocity, and incoming water flow rate. The methodpreferably further comprises comparing the rate of brine consumption tothe rate of brine consumption in a clean electrolytic cell. The cleaningstep optionally comprises using an ultrasonic device and/or using amagnetically actuated mechanical electrode cleaning device, or reversingthe polarity of electrodes in the electrolytic cell, thereby loweringthe pH at a cathode.

The present invention is also an apparatus for producing an oxidant, theapparatus comprising a brine supply, an electrolytic cell, an acidsupply, and a control system for automatically introducing acid from theacid supply into the electrolytic cell. The acid supply preferablycomprises a second electrolytic cell, and the brine supply preferablyprovides brine to the second electrolytic cell during a cleaning cycle.The apparatus preferably further comprises a variable speed brine pump,a carbonate detector, one or more thermowells for measuring atemperature of said electrolytic cell, and/or one or more flowmeters formeasuring the brine flow rate.

The present invention is also an apparatus for producing an oxidant, theapparatus comprising a brine supply, an electrolytic cell, a cleaningmechanism in the electrolytic cell, and a control system forautomatically activating the cleaning mechanism. The cleaning mechanismpreferably is selected from the group consisting of ultrasonic horn,magnetically actuated electrode mechanical cleaning device, and acidicsolution at a cathode surface. The apparatus preferably furthercomprises a device selected from the group consisting of a carbonatedetector, at least one thermowell for measuring a temperature of saidelectrolytic cell, and a flowmeter for measuring a brine flow rate.

The present invention is also a method for cleaning an electrolytic cellcomprising electrodes, the method comprising the steps of reversingpolarities of two or more of the electrodes and providing a cleaningcurrent density to the electrodes which is lower than an operationalcurrent density used during normal operation of the electrolytic cell.During normal operation the electrolytic cell preferably produces aconcentration of free available chlorine greater than approximately fourgrams per liter, more preferably greater than approximately five gramsper liter, and most preferably approximately eight grams per liter. Theoperational current density is preferably greater than approximately oneamp per square inch. The cleaning current density is preferably lessthan approximately 20% of the operational current density, and morepreferably between approximately 10% and approximately 15% of theoperational current density. The providing step is preferably performedfor less than approximately thirty minutes, and more preferably forbetween approximately five minutes and approximately ten minutes. Thereversing step optionally comprises using at least one power supplyrelay or other switching device. The operational current density ispreferably provided by an operational power supply and the cleaningcurrent density is preferably provided by a separate cleaning powersupply. The power producing capacity of the cleaning power supply ispreferably smaller than the power producing capacity of the operationalpower supply. The method preferably further comprises the step ofmonitoring a flow rate of electrolyte through the electrolytic cell. Themonitoring step is preferably performed using a flowmeter, a rotameter,or a pressure transducer, or monitoring a temperature difference acrossthe electrolytic cell via a first thermocouple or thermowell disposed atan inlet of the electrolytic cell a second thermocouple or thermowelldisposed at an outlet of the electrolytic cell. The method preferablyfurther comprises the step of automatically adjusting the flow rate, andpreferably further comprises the step of initiating a cleaning cycle ata predetermined flow rate.

The present invention is also method for cleaning an electrolytic cellcomprising electrodes, the method comprising the steps of reversingpolarities of two or more of the electrodes and providing a cleaningvoltage potential difference to the electrodes which is lower than anoperational voltage potential difference used during normal operation ofthe electrolytic cell. During normal operation the electrolytic cellpreferably produces a concentration of free available chlorine greaterthan approximately five grams per liter. The providing step ispreferably performed for a time between approximately five minutes andapproximately ten minutes. The reversing step preferably comprises usingat least one power supply relay or other switching device. Theoperational voltage potential difference is preferably provided by anoperational power supply and the cleaning voltage potential differenceis preferably provided by a separate cleaning power supply. The methodpreferably further comprises the steps of monitoring a flow rate ofelectrolyte through the electrolytic cell and automatically adjustingthe flow rate.

The present invention is also an apparatus for producing electrolyticproducts, the apparatus comprising an electrolytic cell comprisingelectrodes; a first power supply for providing a first current densityto the electrodes, a second power supply for providing a second currentdensity to the electrodes, the second power supply having an oppositepolarity to the first power supply, wherein the second current densityis smaller than the first current density. The electrolytic cellpreferably produces a concentration of free available chlorine greaterthan approximately five grams per liter. The second current density ispreferably between approximately 10% and approximately 15% of the firstcurrent density. The apparatus preferably further comprises at least onepower supply relay or other switching device, and preferably comprises aflow monitoring device for monitoring a flow rate of electrolyte throughthe electrolytic cell. The flow monitoring device is preferably selectedfrom the group consisting of a flowmeter, a rotameter, a pressuretransducer, a pair of thermocouples, and a pair of thermowells. If apair of thermocouples or thermowells is used, one thermocouple orthermowell is preferably disposed at an inlet of the electrolytic celland another thermocouple or thermowell is preferably disposed at anoutlet of the electrolytic cell. The apparatus preferably furthercomprises an electronically operated valve for adjusting the flow rate.

Objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing, which is incorporated into and form a part ofthe specification, illustrates an embodiment of the present inventionand, together with the description, serves to explain the principles ofthe invention. The drawing is only for the purpose of illustrating apreferred embodiment of the invention and is not to be construed aslimiting the invention. In the drawings:

FIG. 1 is a diagram of one embodiment of a low maintenance on-sitegenerator unit.

FIG. 2 is a schematic of a reverse polarity system for electrolytic cellcleaning.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Best Modes for Carrying Out theInvention

Embodiments of the present invention are methods and devices whereby anon-site generator electrolytic cell is preferably monitoredautomatically for buildup of contaminants on the electrode surfaces, andwhen those contaminants are detected, the electrolytic cell is cleanedautomatically (i.e, without operator intervention), thereby providing asimple, low cost, and reliable process for achieving a highly reliable,low maintenance, on-site generator which does not require the typicaloperator intervention and/or auxiliary equipment (such as a watersoftener) now required for long life of electrolytic cells.

The internal status of the electrolytic cells can be monitoredautomatically by monitoring cell inputs and performance. It is knownthat how much brine a cell consumes is dependent on the amount and typeof film buildup on that given cell. If brine flow is continuouslymonitored, any dramatic change in brine flow to reach a given current ata given voltage is indicative of a potential problem with film buildupwithin a cell. The invention preferably monitors the flowcharacteristics of the brine, incoming water, temperature, etc., todetermine whether or not there has been contaminant buildup within theelectrolytic cell. When potential film buildup is detected in the cellby the control system, the cell is preferably automatically acid washed.

A carbonate detector integrated with an electrolytic cell, automaticacid washing, and device controls may be utilized. A separateelectrolytic cell from the one used to create the mixed oxidant orsodium hypochlorite is preferably used to create the acid on site and ondemand and to provide the acid for removing of contaminants in theelectrolytic cell used for creating the sodium hypochlorite or mixedoxidants. Alternatively a reservoir is used to store concentrated acidonsite for cleaning the cell, and monitoring that acid reservoir andalarming operators when that acid reservoir would need to be refilled,as well as optionally diluting the acid to a desired concentration priorto washing the cell. An ultrasonic cleaning methodology forautomatically removing unwanted contaminants when the contaminants aredetected by the methods described above may also be integrated into thepresent invention.

An embodiment of the present invention is shown in FIG. 1. All of thecomponents of this device are preferably mounted to back plate 15. Thecontrols and power supplies for all the separate components shown inthis embodiment are all preferably contained within control box 5, butmay alternatively be located wherever it is convenient, preferably aslong as there are master controls for the overall operation of theapparatus.

Control box 5 preferably shows the status of the unit via display 10,and the master controls as well as electrical power and/or componentsignals are preferably carried via electrical connections 50 betweencontrol box 5 and the various individual components. Water preferablyenters the system through water entrance pipe 30, and brine preferablyenters the system through brine entrance pipe 25. Brine, preferablystored in a saturated brine silo or tank, is preferably pumped viavariable speed brine pump 20, which is preferably controlled and poweredby electrical connection 50. The brine then preferably passes throughflow meter 35, which can be electrically monitored via electricalconnection 50. The control system can control the flow rate of the brineby increasing the speed of variable speed brine pump 20.

When the electrolytic generator is in normal operation mode and is attarget current and target voltages, the total flow through theelectrolytic cell 55 can be monitored, for example by a flowmeter,rotameter, or pressure transducer, or by monitoring the change intemperature across the electrolytic cell 55 by monitoring inletthermowell 65 and exit thermowell 70. When control box 5 determines thatflow is off target, for example in response to fluctuations in incomingpressure and/or flow to the electrolytic generator, it preferablyautomatically adjusts flow by changing electronically controlled cellinlet valve 6. In this way, the cell can always operate near target flowlevels and will not routinely require measurement or adjustment ofincoming flows.

Data from any of the following sources (or combinations of data from anyof these sources) is preferably used to determine the volumetric flowrate of brine: flow meter 35, carbonate detector 60, electrolytic cell55, acid generating electrolytic cell 45, and/or thermowells 65, 70.Valve 40 can direct flow either to electrolytic cell 55 or to acidgenerating electrolytic cell 45. Valve 40 typically flows an electrolytecomprising diluted brine (as both the concentrated brine and waterinflows have preferably been plumbed together and the brine has beendiluted before it reaches valve 40) to electrolytic cell 55. In thisstandard operating configuration, the system produces, for example,mixed oxidants or sodium hypochlorite.

As contaminants build up on carbonate detector 60, which may be locatedelsewhere according to the present invention, carbonate detector 60sends a series of signals to control box 5, preferably via electricalconnections 50, which indicate whether or not a contaminant film isbuilding up on electrolytic cell 55. When carbonate detector 60indicates that there is contaminant film, control box 5 preferablybegins an acid cleaning cycle in the device, wherein valve 40 isactuated via electrical connection 50 to force diluted brine throughacid generating cell 45, which is also preferably energized by controlbox 5 via electrical connections 50. The system preferably runs brinepump 20 to flow at a rate (as measured by flow meters 35) which has beenoptimized for optimal acid creation in acid generating electrolytic cell45. In this embodiment, the acid created in acid generation cell 45preferably flows through electrolytic cell 55, where it preferablycleans the contaminants, then flows through carbonate detector 60. Thesystem preferably runs in this acid cleaning mode until carbonatedetector 60 sends a signal to control box 5 indicating that the systemis clean and can begin running again in standard mixed oxidant or sodiumhypochlorite production mode. The acid used to clean electrolytic cell55 is preferably dumped to a separate waste drain after flowing throughcarbonate detector 60 instead of dumping it to the oxidant storage tank.Electrolytic cell 55 may optionally be cleaned with an ultrasonic hornand/or a magnetically actuated electrode mechanical cleaning apparatusin addition to or in place of using an acid generating cell.

In an alternative embodiment, concentrated acid is stored in areservoir. During the acid cleaning cycle, control box 5 preferablyactivates a pump or valve to allow flow of the acid to electrolytic cell55. The reservoir is preferably large enough to accommodate manydifferent acid wash cycles. Some of that acid may potentially be dilutedwith standard incoming water to clean electrolytic cell 55.

If carbonate detector 60 (or any other contaminant detecting component)is not used, electrolytic cell 55 preferably may be cleaned on apredetermined cleaning schedule to ensure contaminants do not ruinelectrolytic cell 55. Typically this cleaning schedule would be basedupon the number of hours that the electrolytic cell had been runningsince the last cleaning was completed, and is preferably frequent enoughto ensure that there is no excessive contaminant buildup on theelectrolytic cell.

The rate of brine consumption may optionally be used to determine thepresence of contaminants in electrolytic cell 55. In normal operation ina clean cell, the rate of brine consumption is steady and measurable. Ascarbonate scale builds up within electrolytic cell 55, the carbonatelayer acts as an electrical insulator between the anode and cathodewithin electrolytic cell 55. To compensate for this insulating effect,and to maintain the amperage within electrolytic cell 55, the rate ofbrine consumption increases to increase the conductivity withinelectrolytic cell 55. This increased rate of brine consumption iscompared to the normal rate of brine consumption. Flow throughelectrolytic cell 55 can also be used to measure contaminant buildupwithin electrolytic cell 55. Flow can be measured indirectly bymeasuring the temperature rise through electrolytic cell 55, for exampleby comparing the temperature difference between two thermocouples orinlet thermowell 65 and cell discharge thermowell 70. When carbonatebuildup is detected by any of these means, electrolytic cell 55 can becleaned by any of the methods or components described above. Brineconsumption may be measured using brine flow rate, tachometer rates ofbrine pump 20, or incoming water flow rates.

In addition to (or instead of) the cleaning methods described above, theelectrolytic cell may optionally be cleaned by reversing the polarity ofthe electrodes in electrolytic cell, while flowing electrolyte throughthe electrolytic cell or not, and preferably for a very short duration.Reversing the polarity of the electrodes, preferably at low currentdensities, lowers the pH at the cathode, which dissolves and removes thecontaminants. However, the dimensionally stable anode in the chlorine (4to 8 gm/L) producing electrolytic cell described herein typicallyoperates well at high current densities (up to 2 amps per square inch),but would fail quickly if polarity were reversed at the same currentdensity. Thus it is preferable to use a separate power source at lowercurrent density and/or lower plate to plate voltages to clean the cellin reverse polarity mode, which is only operated when the normalchlorine production operational mode is in standby, so that the primaryanode coating remains undamaged. Under these conditions, cleaning cyclesof less than 30 minutes can be achieved, preferably ranging betweenapproximately 5 minutes and 10 minutes. Industry experience indicatesthat cell cleaning intervals of less than a week would represent anunfavorable situation where the feed water to the electrolytic cell, orthe salt used to make the brine solution, would typically be poorquality. Intervals between cleaning of greater than one week are clearlythe industry norm. Under the worst case condition of cleaning once perweek, the loss of system duty cycle (production operation mode) wouldstill be negligible.

In any embodiment using reverse polarity to clean the electrolytic cell,both the anode and cathode surfaces of both primary and bi-polarelectrodes are preferably coated with an appropriate dimensionallystable anode coating.

FIG. 2 is a schematic of an embodiment of a system for implementingreverse polarity cleaning. Electrolytic cell 130 comprises anode 134 andcathode 132 with electrolyte flowing in at the bottom and oxidantflowing out at the top of the cell. In normal operation, electrolyticcell 130 has electrical energy applied to anode 134 and cathode 132 viamain power supply 136. Periodically, electrolytic cell 130 will becleaned by reversing the polarity on anode 134 and cathode 132,effectively making anode 134 the cathode, and cathode 132 the anode. Inthe normal mode of production where the system is producing a chlorinebased disinfectant, the current density on anode 134 is preferablybetween approximately 1 and 2 amps per square inch. To avoid damage toanode 134 during the reverse polarity cleaning step, the current densityis preferably less than approximately twenty percent of the normaloperating current density range, and more preferably between about 10%and 15% of the normal operating current density range. Because thereverse polarity cleaning operation operates at much lower powersettings, power is preferably supplied by cleaning power supply 138,which can be much smaller than main power supply 136. Power from mainpower supply 136 is transferred to electrolytic cell 130 preferably viamain power cables 144. Power from cleaning power supply 138 istransferred to electrolytic cell 130 preferably via cleaning powercables 146. The power supplies are preferably isolated via main powersupply relay 140 and cleaning power supply relay 142. In normaloperation when chlorine is being produced within electrolytic cell 130,main power supply 136 is energized and main power supply relay 140 isclosed. To avoid backflow of current to cleaning power supply 138 withthe wrong polarity, cleaning power supply relay 142 is open. Likewise,when electrolytic cell 130 is operating in cleaning mode, cleaning powersupply 138 is energized, main power supply 136 is de-energized, mainpower supply relay 140 is open, and cleaning power supply relay 142 isclosed. By utilizing less current density and/or lower potentials onanode 134 during the short cleaning cycle, damage to anode 134 orcathode 132 due to the cleaning cycle is negligible.

An alternative embodiment to the one shown in FIG. 2 uses the main powersupply 136 to provide power for normal operation as well as the cleaningcycles. This approach preferably employs the use of power supply relays142 or other switching devices to reverse the polarity. Typically thisapproach requires the electrolytic cell brine concentrations during thecleaning cycle to be much less than in normal operation. With thisapproach, however, it is still preferable that the cleaning cycle beperformed at lower current densities and/or lower potentials for shortperiods of time.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverall such modifications and equivalents. The entire disclosures of allpatents and publications cited above are hereby incorporated byreference.

1. A method for cleaning an electrolytic cell comprising electrodes, themethod comprising the steps of: reversing polarities of two or more ofthe electrodes; and providing a cleaning current density to theelectrodes which is lower than an operational current density usedduring normal operation of the electrolytic cell.
 2. The method of claim1 wherein during normal operation the electrolytic cell produces aconcentration of free available chlorine greater than approximately fourgrams per liter.
 3. The method of claim 2 wherein during normaloperation the electrolytic cell produces a concentration of freeavailable chlorine greater than approximately five grams per liter. 4.The method of claim 3 wherein the concentration of free availablechlorine is approximately eight grams per liter.
 5. The method of claim1 wherein the operational current density is greater than approximatelyone amp per square inch.
 6. The method of claim 1 wherein the cleaningcurrent density is less than approximately 20% of the operationalcurrent density.
 7. The method of claim 6 wherein the cleaning currentdensity is between approximately 10% and approximately 15% of theoperational current density.
 8. The method of claim 1 wherein theproviding step is performed for less than approximately thirty minutes.9. The method of claim 8 wherein the providing step is performed forbetween approximately five minutes and approximately ten minutes. 10.The method of claim 1 wherein the reversing step comprises using atleast one power supply relay or other switching device.
 11. The methodof claim 1 wherein the operational current density is provided by anoperational power supply and the cleaning current density is provided bya separate cleaning power supply.
 12. The method of claim 11 wherein apower producing capacity of the cleaning power supply is smaller than apower producing capacity of the operational power supply.
 13. The methodof claim 1 further comprising the step of monitoring a flow rate ofelectrolyte through the electrolytic cell.
 14. The method of claim 13wherein the monitoring step is performed using a flowmeter, a rotameter,or a pressure transducer, or monitoring a temperature difference acrossthe electrolytic cell via a first thermocouple or thermowell disposed atan inlet of the electrolytic cell a second thermocouple or thermowelldisposed at an outlet of the electrolytic cell.
 15. The method of claim13 further comprising the step of automatically adjusting the flow rate.16. The method of claim 13 further comprising the step of initiating acleaning cycle at a predetermined flow rate.
 17. A method for cleaningan electrolytic cell comprising electrodes, the method comprising thesteps of: reversing polarities of two or more of the electrodes; andproviding a cleaning voltage potential difference to the electrodeswhich is lower than an operational voltage potential difference usedduring normal operation of the electrolytic cell.
 18. The method ofclaim 17 wherein during normal operation the electrolytic cell producesa concentration of free available chlorine greater than approximatelyfive grams per liter.
 19. The method of claim 17 wherein the providingstep is performed for a time between approximately five minutes andapproximately ten minutes.
 20. The method of claim 17 wherein thereversing step comprises using at least one power supply relay or otherswitching device.
 21. The method of claim 17 wherein the operationalvoltage potential difference is provided by an operational power supplyand the cleaning voltage potential difference is provided by a separatecleaning power supply.
 22. The method of claim 17 further comprising thesteps of monitoring a flow rate of electrolyte through the electrolyticcell and automatically adjusting the flow rate.
 23. An apparatus forproducing electrolytic products, the apparatus comprising: anelectrolytic cell comprising electrodes; a first power supply forproviding a first current density to said electrodes; a second powersupply for providing a second current density to said electrodes, saidsecond power supply having an opposite polarity to said first powersupply; wherein the second current density is smaller than the firstcurrent density.
 24. The apparatus of claim 23 wherein said electrolyticcell produces a concentration of free available chlorine greater thanapproximately five grams per liter.
 25. The apparatus of claim 23wherein the second current density is between approximately 10% andapproximately 15% of the first current density.
 26. The apparatus ofclaim 23 further comprising at least one power supply relay or otherswitching device.
 27. The apparatus of claim 23 further comprising aflow monitoring device for monitoring a flow rate of electrolyte throughsaid electrolytic cell.
 28. The apparatus of claim 27 wherein said flowmonitoring device is selected from the group consisting of a flowmeter,a rotameter, a pressure transducer, a pair of thermocouples, and a pairof thermowells.
 29. The apparatus of claim 28 wherein one thermocoupleor thermowell is disposed at an inlet of said electrolytic cell andanother thermocouple or thermowell is disposed at an outlet of saidelectrolytic cell.
 30. The apparatus of claim 27 further comprising anelectronically operated valve for adjusting the flow rate.